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Heil furnace issues - interesting fix

02-12-2008, 06:57 AM

It has been really cold in my area this winter - especially in the last few days - single digit temps., wind, etc. Last night, my house seemed cold but I heard the furnace running. Actually, it was the vent motor - the burner was not lighting. Furnaces always seem to act up at 9:00 PM on the coldest day of the year....

I shut everything down and turned it back on, the burner lit, and the blower came on and then after a few minutes, it went out. I looked for the wiring diagram and it was nowhere to be found... so I decided to check the pilot assembly and flame sensor. I took the pilot assembly out and cleaned the flame sensor and put it back in and turned the power on. At this point, I had the front panel of the burner housing off in order to observe the pilot, flame sensor, etc. All seemed well until I buttoned up the burner housing. I noticed a plastic plug laying on the bottom of the unit that was the same size as the hole in the side of the burner housing. I reset the unit and after the burner lit, I installed the plug in the hole in the side of the burner housing next to the pressure switch tube connector. I felt a strong vacuum and as soon as I installed the plug, the flame went out.

I then removed the fresh air intake pipe and reset the unit - everything functioned properly. I installed the plug in the side of the housing and moved the intake pipe into position and the flame started to go out.

Long story short, ice was blocking the intake pipe outside. It wasn't much but after I cleaned it out, the furnace functioned fine.

I awoke this morning to a cool house and the sound of the furnace vent motor running... No burner flame was present so I checked the intake and it was choked off with ice again...

Is there a minimun distance from the furnace exhaust to the intake? The intake and exhaust pipes are only 12" apart. I am starting to think the intake is drawing some of the moisture from the exhaust and it is freezing in the intake.

Comment

12" apart between the intake and exhaust? Jeesh...I hope the Furnace manufacturer didn't spec that - I wouldn't think they would spec something like that. If they did then well....you're proof in the pudding that it should be 24" minimum or even more. Is your furnace a high efficiency unit - even worse in this case.

I am assuming the penetration for the intake/exhaust is on the side of your house somewhere? Is it PVC/ABS or some type of B-vent penetration?

Comment

12" apart between the intake and exhaust? Jeesh...I hope the Furnace manufacturer didn't spec that - I wouldn't think they would spec something like that. If they did then well....you're proof in the pudding that it should be 24" minimum or even more. Is your furnace a high efficiency unit - even worse in this case.

I am assuming the penetration for the intake/exhaust is on the side of your house somewhere? Is it PVC/ABS or some type of B-vent penetration?

The intake/exhaust pipes exit the basement through the rim joist at the back of the house. It's a high efficiency unit.

Can the intake be extended slightly? Maybe that would be the easiest solution.

Comment

We put ours as close together as possible. Amana's installation instructions say 3" minimum and 24" maximum. The intake should have a downward pointing elbow, and the exhaust should extend just an inch or two past the intake. We NEVER have problems with recirculation unless the snow gets too deep, or someone stacks lawn chairs in front of the pipes. (just this week)

I'll try to get some pictures to share.
I would not extend the intake. The exhaust plume shoots out quite a distance; if you extend the intake you're going to have the same problem.
If the pipes are 12" apart, then I might extend the flue pipe a foot or so and see if this helps.

Comment

We put ours as close together as possible. Amana's installation instructions say 3" minimum and 24" maximum. The intake should have a downward pointing elbow, and the exhaust should extend just an inch or two past the intake. We NEVER have problems with recirculation unless the snow gets too deep, or someone stacks lawn chairs in front of the pipes. (just this week)

I'll try to get some pictures to share.
I would not extend the intake. The exhaust plume shoots out quite a distance; if you extend the intake you're going to have the same problem.
If the pipes are 12" apart, then I might extend the flue pipe a foot or so and see if this helps.

I think the exhaust pipe extends slightly longer than the intake and both have a downward 45 degree elbow on them.

The snow is not built up next to the pipes but the bank is about two feet away. I'll clear it away as much as I can and see if that helps. Thanks for the input.

Comment

If you can try extending the exhaust and have it a good bit higher up than the intake. Also try to have it blow more outward. You might take off the 45 elbow and replace it with a 22-1/2 degree one. There's loads of moisture in the exhaust and with it being cold the ice problems in your intake most likely are from this. In addition you do not want to be sucking exhaust fumes back into your furnace. I see far too many installations where they are run too close to each other.

Do clean up the snow so you have lots of air around both the intake and exhaust outside.

Comment

Every furnace needs to be vented according to the manufacturers specs. They all have their own methods that need to be followed. From what the OP is describing, this furnace was not vented to spec. Adding something here, or taking away something there is not the right way to fix this problem. Moving the intake further away from the exhaust is not recommended by any manufacturer I have ever seen. Most, want the intake and exhaust fairly close to each other with the exhaust pipe being 8 to 12 inches longer than the intake. The theory is, the exhaust when being forced out will create a venturi effect and pull in fresh air behind it. Fresh air which can be sucked right into the intake.

I never individually 2 pipe a furnace. A concentric vent kit either through the roof, or through the box-sill is the only way I will 2 pipe any furnace. I'd rather have a single pipe system than a 2 penetration 2 pipe.

Comment

My next step is to get a copy of the installation specifications and see if my installation conforms. I'd like to get a wiring diagram for the unit as well since there was not one to be found on the unit.

There is also a 6" diameter round duct that beings in air from the outside and is piped to within 12-18" off the basement floor. I expect it is to provide a source of make up air in case the house is sealed too tight but geeze - the cold air just pours in and makes the basement cold...